1. Field of the Invention
The present invention is related to a valve of a storage tank for transporting oils or chemical compounds. In more detail, the present invention is related to a valve for maintaining the pressure state of the above storage tank to be always safe by preventing supersaturated pressure or negative pressure, which is the opposite phenomenon of supersaturated pressure, generated in the storage tank of transportation vessels such as an oil tanker. The valve in the present invention also prevents entering of flame generated outside of the storage tank into the storage tank.
2. Description of the Prior Art
Usually, supersaturated pressure and negative pressure (vacuum phenomenon) are generated frequently in storage tanks keeping various oils or chemical compounds. That is, it is possible that the pressure in a storage tank is increased by volatile gases from various oils or chemical compounds stored in the storage tank, however, pressure may be varied according to the change in temperature due to the difference in climate occurring in each district where an oil tanker or a transportation vessel of chemical compounds sails. In almost all such cases, supersaturated pressure is generated. And if an oil or chemical compound is discharged from the storage tank by pumping, the pressure is lowered in the storage tank and negative pressure (vacuum phenomenon) is generated.
If the pressure is changed in a closed space, not only oils or chemical compounds which are highly explosive and inflammable become unstable, but also there is a high probability that explosion or fire will occur, and it is possible to have a serious accident if the above storage tank is exploded. Therefore, every storage tank keeping oils or chemical compounds is subject to be equipped with vent pipes which are connected to outside at all times. However, since these vent pipes are always open, a large amount of oils or chemical compounds are evaporated through them. This eventually implies economical loss as well as contaminating air.
There have been a few inventions to resolve the above-identified problems. They include Korean Utility Model Registration No. 125817 entitled "A valve gear for absorbing or discharging air of a transportation tank of oils or chemical compounds" owned by the applicant of the present invention, and U.S. Pat. No. 5,060,688. However, in these inventions, the suction means of external air or storage tank and the discharging means of expanded gases which discharges volatile gases from the storage tank are separated from each other crossing at a right angle and are connected to each other by means of other connection pipes. They are therefore disadvantageous in that they occupy a large installation space. Also, there is a problem of increasing the weight of a vessel if the above conventional equipments are installed at a transportation vessel since their own weights are considerable. Since more than tens of these equipments are to be installed at one vessel, their weights are not insignificant. Further, it has been inconvenient to repair them since their manufacture and assembling take a long time in terms of processing, their unit prices are increased, and their structures are unreasonably complicated. Still further, it has been difficult to clean foreign materials which are fixed inside of the equipment as it is used.